In the pharmaceutical industry there is a need to volumetrically measure small volumes of powdered solids and to fill them into individual vials for later constitution with sterile liquid materials and injection of the resulting solution into patients needing treatment. In one method of carrying out the filling of vials with dry solids, there is provided a device comprising a filling wheel having a series of radially aligned cylindrical measuring cavities with the open end facing the circumference of said filling wheel. The volume of the measuring cavity is controlled by a filter assembly which forms the bottom of the measuring cavity. The filter assembly is coupled to a hollow, adjustable cylinder connected by a threaded stem to the filling wheel hub permitting adjustment of the position of the filter assembly in the measuring cavity. The filter assembly comprises a molded nylon cylinder slidably enclosed in said measuring cavity, coupled at one end to said adjustable cylinder and closed at the other end by a fine mesh nylon screen heat sealed thereto, said nylon screen forming the bottom of the measuring cavity. The nylon screen has openings small enough to prevent passage of powdered solid but large enough to permit gas flow.
As the wheel rotates, the open end of the cavity is positioned under a filling hopper and simultaneously vacuum is applied through the hub to the filter assembly to draw the powder into the cavity. As the wheel continues to rotate, a suitable receptacle is positioned under the open end of the filled cavity and nitrogen pressure is applied to the filter and to expel the measured amount of powder in the receptacle. However, the prior art filter assembly caused a relatively high failure rate in that an unacceptable variation in the amount of delivered product occurred. It is believed that this failure is caused by the uneven packing of solids in the cavity resulting from the uneven distribution of gas flow.